1. Field of the Invention
The invention relates to a semiconductor device and an electronics device composed of the same.
2. Description of the Related Art
In recent years, portable electronics devices (a mobile phone, etc.) driven with a battery have been popular. There has been a strong demand for semiconductor devices mounted in the portable electronics devices to operate at a high-speed with low power consumption in order to realize advanced functions of the electronics devices and a long-term use of a battery.
Furthermore, along with the miniaturization of the structure of semiconductor devices, a power supply voltage applied to the semiconductor devices has been lowered. A small difference between the power supply voltage and a threshold voltage of the transistor due to low power supply voltage makes it difficult for the transistor to turn on, thereby decreasing the operating speed of the semiconductor device. To realize the high-speed operation of the semiconductor device with a low power supply voltage, it is necessary to set low the threshold voltage of the transistor. However, sub-threshold leakage current (off-state leakage current) of the transistor during an off state increases as the threshold voltage of the transistor lowers or an operation temperature rises. As a result, at a low set threshold voltage of the transistor, the high-speed operation of the semiconductor device is achievable, however, power consumption in the standby period of the semiconductor device increases.
In a semiconductor device including a plurality of circuit blocks, for example, a threshold voltage of the transistor within the circuit block is set low in order to realize the high-speed operation, and a switch transistor (a leakage cut-off transistor) is disposed between the power supply terminal of the circuit block and the power supply line to turn on in the active period and turn off in the standby period, in order to achieve low power consumption by reducing off-state leakage current of the transistor in the standby period.
Also, WO00/11486 discloses a technique to easily, accurately detect whether there is leakage current larger than a predetermined value in a semiconductor device.
The semiconductor device with the function of curtailing off-state leakage current (a leakage cut-off function) using the leakage cut-off transistor includes a test mode (the leakage cut-off function is invalid) in which the leakage cut-off transistor is constantly turned on regardless of an operation state of the semiconductor device, in addition to a normal mode (the leakage cut-off function is valid) in which the leakage cut-off transistor is turned on according to an operation state of the semiconductor device.
In a test, process of the semiconductor device as described above, a function test is performed in the normal mode. When a result of the test is a fail, the function test is performed again in the test mode. It is possible to determine whether defects have occurred due to the leakage cut-off function based on the result of the test, pass/fail, in the test mode. It is, however, not possible to find details of the defects such as to identify a circuit block having the defects due to the leakage cut-off function from a plurality of circuit blocks. Because of this, defect analysis cannot be efficiently performed, consuming an enormous amount of time.